The present invention generally relates to body implantable cardiac lead assemblies. More specifically, the invention relates to implantable leads with fixing helixes. Yet more specifically, the invention relates to implantable leads with means for actuating the fixing helix to automatically screw into body tissue.
Numerous types of implantable lead assemblies are known for use with cardiac pacemakers having different types of structures for fixing the tip of the lead to cardiac tissue. In one type of lead assembly, a fixing helix is positioned at the distal end of an implantable lead so that the lead can be attached to body tissue, such as the heart, by appropriate rotation of the helix such that the helix screws into the body tissue. Various structures for rotating the helix have been devised.
U.S. Pat. No. 4,217,913 discloses an implantable endocardial lead assembly with a protected, extendable, fixing helix. The fixing helix is extendable out of the distal end of the lead assembly through a tissue covering the lead. In one embodiment, the lead is provided with a spring loaded stylet such that the helix can be automatically driven by the spring in rotating fashion to automatically engage and secure into heart tissue. A threaded arrangement between the stylet and the outer casing of the lead ensures that the helix rotates only a predetermined distance.
In operation, prior to insertion of the stylet, a knob is wound a number of turns to store rotational energy in a spring. Upon release, the spring rotates a rotor body an approximate number of turns. A compressor spring assists in imparting forward rotational movement and to prevent backlash of the rotor body.
U.S. Pat. No. 4,649,938 discloses an implantable lead assembly having an extendable/retractable fixing helix. The helix extends beyond the tip of the lead only upon the application of an external force by a stylet on a carrier bobbin on which the helix is mounted. Otherwise, biasing means also positioned within the lead, urges the fixing helix to a retracted position within the distal tip of the lead assembly. Rotation of the helix is effected manually. The carrier bobbin and lead are provided with complementary octagonal shapes, much like a socket wrench and not respectively so that rotation of the lead will cause rotation of the bobbin.
U.S. Pat. No. 4,858,623 discloses an active fixing mechanism for the lead assembly of an implantable endocardial lead. The active fixing mechanism includes a tissue stimulating electrode with a rigid hook for engaging tissue, which hook is pivotally fastened to the lead in the vicinity of the electrode. The tip of the hook is normally resiliently urged into a recess and lead adjacent to the electrode. A mechanism is coupled to the lead to permit the normal bias of the hook tip to be selectively overcome to position the hook outwardly of the lead. In this position, the hook is deployed to engage tissue in the vicinity of the electrode. The force applied to deploy the hook may be removed to allow the hook to move back into the recess under the normal bias. Sufficient force supplied to the hook while deployed along the axis of the lead, will cause the hook to assume a position beyond the distal end of the lead, in which it is precluded from engaging tissue.
U.S. Pat. No. 4,886,074 discloses an implantable endocardial lead assembly with an extendable helix and electrode wherein the lead assembly has an electrode head which includes a fixing helix for implantation into tissue, a prelocking spring that upon release causes the helix to rotate, as well as a releasable blocking mechanism that prevents rotation. The electrode head includes all of the elements required for the blocking function of the mechanism and can be released by axial movement of the fixing helix or a connector block associated with the helix.
In an embodiment, all of the elements of the blocking mechanism are directly attached to the fixing helix, the connector block, the electrode lead, or the insulating sheath, such that the release of the block is accomplished by axial movement of the helix and the connector block from the area of the blocking mechanism at the electrode head or the insulating sheath. Small axial forces are sufficient to release the blocking mechanism and axial movement of the fixing spiral or the connector block can be accomplished either mechanically, hydraulically, or pneumatically.
It is discussed that mechanical release blocking of the mechanism can be accomplished by means of an axial shifting movement of a stylet.
In one embodiment, the helix is secured to a rotatable connector block which itself is positioned within the sleeve. A pin protruding from the sheath engages a small slot in the connector block to prevent rotation. However, the insertion of a stylet will cause the block to move sufficiently axially such that the pin is disengaged and then the connector block and the helix secured thereto rotate under the influence of a stored torsional force provided by a prestressed spring.
U.S. Pat. No. 4,924,881 discloses an implantable endocardial lead with a retractable fixing helix wherein the fixing helix comprises a sharpened helix which can be repeatedly both retracted within a distal end of the lead and displaced outside the lead. A threaded stylet passes through a sheath from a proximal end of the lead to the distal end of the lead, where the threaded stylet is screwed into a piston supporting the helix. When the helix is in an exposed position, torque can be transmitted from the proximal end of the lead through the distal end to the piston and then to the helix to screw the helix into the endocardial tissue.
German OS 32 30 081 discloses a lead assembly with a fixing helix arrangement designed for use With a heart pacemaker including a catch which locks the helix into an extended position.
The disclosures of all of these patents are incorporated herein by reference.